As shown in FIG. 1, a typical moving coil loudspeaker consists of a diaphragm, driving devices, and suspension devices. The diaphragm F, when pushed and pulled by the driving devices, vibrates airs and thereby creates sound waves. The diaphragm can have a cone or dome shape. The driving devices include a magnet A, a polar plate B, a top iron C, a gap D, and a voice coil E. The diaphragm is attached to the voice coil. The suspension devices include a surround and a spider G. The surround is a flexible material that attaches the diaphragm's outer rim to the loudspeaker's frame (not shown in FIG. 1). The spider is also a flexible material having a ripple shape. The spider holds the voice coil in position, but allows the voice coil to move freely back and forth.
Running alternating electrical current through the voice coil creates a magnetic field around the voice coil. The magnetic field interacts with the magnet so that the voice coil is attracted or repelled by the magnet. This pushes the voice coil back and forth rapidly, like a piston. When the voice coil moves, it pushes and pulls the attached diaphragm. The diaphragm vibrates airs in front of the loudspeaker and thereby creates sound waves.
The spider functions just like a cushion in an automobile's suspension system. The spider has to be strong enough so that it can sustain the voice coil's vibration without becoming deformed. The spider also has to be flexible enough so that the voice coil can move freely. The two qualities of a spider therefore have significant impacts on the loudspeaker's performance.
FIG. 2 is a stereographic diagram showing a conventional spider G according to a prior art. As shown in FIG. 2, the spider has a plurality of concentric, circular corrugations of crest G1 and trough G2. The spider's center hole is for holding the voice coil (not shown in FIG. 2) while the spider's outer rim is attached to the loudspeaker's frame (not shown in FIG. 2). As shown in FIG. 3A, the spider shows a continuous wave shape in a cross section along a radial direction (along an line A—A of FIG. 2). When the spider is put under external forces, the spider's cross sections perpendicular to the spider's radius as shown in FIG. 3B (along line B—B of FIG. 2) have enough strength. However, the spider's cross sections aligned with the spider's radius as shown in FIG. 3A (along line A—A of FIG. 2) do not have enough strength. Due to mechanical factors or the loudspeaker is not placed on a level location, external forces applied on a spider are not always uniform. After a period of time, the conventional spider may become deformed and thereby its effectiveness for suspending the voice coil is impaired.